Whole-Genome Resequencing of a Worldwide Collection of Rapeseed Accessions Reveals the Genetic Basis of Ecotype Divergence

Rapeseed (Brassica napus),an important oilseed crop,has adapted to diverse climate zones and latitudes by forming three main ecotype groups,namely winter,semiwinter,and spring types. However,genetic variations underlying the divergence of these ecotypes are largely unknown. Here,we report the global pattern of genetic polymorphisms in rapeseed determined by resequencing a worldwide collection of 991 germplasm accessions.A total of 5.56 and 5.53 million singlenucleotide polymorphisms (SNPs)as Well as 1.86 and 1.92 million InDels were identified by mapping reads to the reference genomes of "Darmor-bzh"and "Tapidor,"respectively.We generated a map of allelic drift paths that shows splits and mixtures of the main populations,and revealed an asymmetric evolution of the two subgenomes of B.napus by calculating the genetic diversity and linkage disequilibrium parameters.Selective-sweep analysis revealed genetic changes in genes orthologous to those regulating various aspects of plant development and response to stresses.A genome-wide association study identified SNPs in the promoter regions of FLOWERING LOCUS T and FLOWERING LOCUS C orthologs that corresponded to the different rapeseed ecotype groups. Our study provides important insights into the genomic footprints of rapeseed evolution and flowering-time divergence among three ecotype groups,and will facilitate screening of molecular markers for accelerating rapeseed breeding.

Agronomical selection on loss-of-function of GIGANTEA simultaneously facilitates soybean salt tolerance and early maturity

Salt stress and flowering time are major factors limiting geographic adaptation and yield productivity in soybean(Glycine max).Although improving crop salt tolerance and latitude adaptation are essential for efficient agricultural production,whether and how these two traits are integrated remains largely unknown.Here,we used a genome-wide association study to identify a major salt-tolerance locus controlled by E2,an ortholog of Arabidopsis thaliana GIGANTEA(GI).Loss of E2 function not only shortened flowering time and maturity,but also enhanced salt-tolerance in soybean.E2 delayed soybean flowering by enhancing the transcription of the core flowering suppressor gene E1,thereby repressing Flowering Locus T(FT)expression.An E2 knockout mutant e2^(CR) displayed reduced accumulation of reactive oxygen species(ROS)during the response to salt stress by releasing peroxidase,which functions in ROS scavenging to avoid cytotoxicity.Evolutionary and population genetic analyses also suggested that loss-of-function e2 alleles have been artificially selected during breeding for soybean adaptation to high-latitude regions with greater salt stress.Our findings provide insights into the coupled selection for adaptation to both latitude and salt stress in soybean;and offer an ideal target for molecular breeding of early-maturing and salt-tolerant cultivars.